// Symbol

const sm1 = new Symbol("13213")
const sm2 = new Symbol("13213")
console.log(sm1 === sm2) // false

const obj = {
    [sm1]: 4134546,
    [sm2]: "fdsfs"
}

const s1 = new Symbol.for("foo")
const s2 = new Symbol.for("foo")
// s1 === s2  true

// Object.keys() 和 for in  无法获取Symbol 类型
// 可通过下列方法获取
Object.getOwnPropertySymbols(obj)
